Answer to Question #153021 in General Chemistry for Abedalrahman Al Addassi

Question

3. Describe the effect of the following factors, whether the increase, decrease, or has no effect on the reported value of Mg to O mole ratio:
a. If carbon is deposited on the crucible’s surface (due to improper heating) and the crucible with contents is weighed without removing the carbon residue.
b. If the magnesium oxide ash is not dried completely.
c. If rapid oxidation of magnesium occurs by too much air, and some Mg is lost.
d. If air is not allowed sufficiently to react with Mg.

Answer 1

a). As part of the procedure for the determination of the sulfate content of an unknown sample it will be necessary to accurately determine the empty weights of a set of crucibles. This is accomplished by first cleaning the crucible and then heating them in the flame of a Tirrel burner. They are then cooled and weighed. This process of heating and cooling is repeated until successive weighings agree to within 0.2mg. The procedure will, in addition, acquaint the student with the use of the analytical balance and the proper use of the desiccator. Be sure that you read the appendix section dealing with the use of desiccator.

b). Students weigh magnesium and heat it in a crucible. The magnesium reacts with oxygen to produce the oxide. Students see there is an increase in mass and can use the results to find the formula of magnesium oxide

c). When magnesium reacts with oxygen, it produces light bright enough to blind you temporarily. ... As a result of this exothermic reaction, magnesium gives two electrons to oxygen, forming powdery magnesium oxide (MgO).

d). the ratio of Mg-to-O is close enough to 1-to-1. In the second example, the product is slightly magnesium-rich; the ratio of Mg-to-O is greater than the 1-to-1 expected. A magnesium-poor product would have a ratio of Mg-to-O that is less than the 1-to-1 expected.